Field of the Invention
The present invention relates to a pumping loss calculation device for an internal combustion engine, which has a variable valve mechanism which is capable of changing the opening timing of an exhaust valve.
Description of the Related Art
Conventionally, as the control device of this kind for controlling the pumping loss of the engine, one disclosed in the Publication of Japanese Patent No. 4609279 is known. This control device controls the pumping loss of the engine by controlling a variable valve mechanism which changes a valve opening characteristic of an exhaust valve, and a throttle valve which is disposed in an intake passage. For example, during the fuel cut operation, if it is determined that deceleration is requested, there are simultaneously performed an exhaust valve opening timing (EVO) advance control for advancing the EVO such that it becomes slightly earlier than a middle stage or its vicinity of an expansion stroke, and a throttling control for throttling a throttle valve.
The exhaust valve is opened according to this EVO advance control in the middle of the expansion stroke, so that an in-cylinder pressure is suddenly lowered to the atmospheric pressure, whereby positive work done is significantly reduced and the pumping loss is relatively increased. Further, negative pressure in the intake stroke is increased by the throttling control, whereby the pumping loss is increased. Furthermore, in this control device, a sum of the pumping loss by the EVO advance and the pumping loss by the throttling control is calculated, and the EVO advance control and the throttling control continue to be performed until the sum reaches a target value. This makes it possible to obtain a required pumping loss, and ensure an engine brake force according to the deceleration request.
The pumping loss of the engine acts as a loss of positive work done which is performed by compression and expansion of gases in the cylinder, and hence even though the combustion torque generated by the compression and expansion of gases is the same, the net torque output from the engine varies with the pumping loss. Therefore, when performing cooperative control using the output torque of the engine, such as traction control or stability control of the vehicle by distributing a driving force from the engine to wheels, it is essential to calculate the pumping loss of the engine with high accuracy.
However, the above-described conventional control device controls the pumping loss of the engine merely by controlling the EVO such that it is advanced. Further, although the Publication of Japanese Patent No. 4609279 mentions calculation of the pumping loss caused by advancing of the EVO, there is disclosed no specific method of calculating the pumping loss. Therefore, it is impossible to calculate the pumping loss with high accuracy.